Apparatus for preparing abrasive articles



Oct. 28, 1958 w. JOHNSON APPARATUS FOR PREPARING ABRASIVE ARTICLES Filed Sept. 1', 1955 III 1/ IIIIIIIIII IAWENTOR. jQwzmm 0% KM 4 ATTORNE Unite APPARATUS FOR PREP G ABRASIVE ARTICLES Application September 1, 1955, Serial No. 532,083

Claims. (Cl. 118-623 This invention relates to the preparation of abrasive articles, and more specifically to an apparatus and method for magnetically orienting and distributing abrasive grains upon suitable adhesive-coated articles such as backing sheets, discs and the like.

In distributing abrasive granules or grains upon'adhesive-carrying articles, it is desirable to orient the generally elongated and sharp-edged grains so that the sharpest and most pointed ends of these grains all face upwardly or in the same direction from the backing articles. While electrostatic methods have been devised to orient abrasive grains, these methods have proved unsatisfactory in several respects. For example, when abrasive grains are distributed upon an article carrying an electrostatic surface charge, the electrostatic charge bridges the surface irregularities of the article and prevents the abrasive grains from embedding themselves within the (lips, shallows or cracks of the adhesive covered article. When that article is later used for sanding, grinding or cutting, these poorly secured grains are quickly loosened and detached from their backing, thereby greatly reducing the performance and effectiveness of the abrasive article for the intended purposes.

Furthermore, it is well known that electrostatic charges upon irregularly shaped particles tend to accumulate and escape from the most pointed ends of those particles. When electrostatically charged abrasive grains are at tracted by an opposite charge carried by a suitable backing article or sheet, the particles orient themselves so that their most pointed ends are directed toward that article and become embedded in the adhesive coating carried thereby. Therefore, when electrostatic orientation methods are employed, the most suitable grinding or cutting edges of the abrasive particles are often embedded in the adhesive coating of the backing article.

A main object of the present invention is to overcome the disadvantages of present methods for preparing abrasive articles, and particularly those disadvantages mentioned above. Another object is to provide an apparatus and method for magnetically orienting abrasive particles so that the sharpest portions of those particles are presented at the working surface of the abrasive article produced thereby. A further object is to magnetically orient and direct abrasive particles upon an adhesive carrying backing article, so that the particles are firmly secured within the shallows and surface irregularities of that article.

A still further object is to provide an apparatus and method for orienting and securing generally elongated and non-magnetic abrasive grains upon an adhesive covered surface so that the longitudinal axes of those grains extend in the same direction from that surface. An additional object is to provide a method and apparatus for mounting the oriented abrasive grains in spaced relation upon a suitable backing article. Other objects will appear from the specification and drawings, in which:

. Figure 1 is a partly sectional and somewhat diagrammatic side view of an apparatus embodying the present atent ice invention; Figure 2 is a broken and partly diagrammatic end view of the apparatus taken along lines 2-2 of Fig ure 1; and Figure 3 is a broken and diagrammatic side view illustrating operational details of the present invention.

In the embodiment of my invention represented in the drawings, the numeral 10 designates a hopper having a chamber 11 and a discharge opening 12 at the lower portion thereof. The hopper is preferably formed from panels of sheet metal, welded or otherwise suitably secured to each other, and is mounted upon horizontally extending beams 13 of a frame (not shown). Within chamber 11 and adjacent front wall or panel 14 of the hopper, is a vertically adjustable door or shield 15. A

connector 16 carried by the shield extends through a slot or opening 17 in the front wall, and is joined at its forward end to a vertically extending threaded shaft 18. Shaft 1% is in turn received by arm 19 secured to front wall 14 and is adjustably mounted upon that arm by nut 20.

Adjacent each of the side walls 21 of the hopper, and welded or otherwise secured thereto, is a connecting plate 22 which rotatably supports a shaft 23 and drum 24 below the discharge opening 12 of the hopper. The drum is positioned so that particles falling through the discharge opening of hopper 1i) strike the curved periphery of the drum and are scattered downwardly and forwardly as the drum is rotated. While no specific means are shown for rotating drum 24, it will be understood that any suitable driving means, such as an electric motor, may be used for that purpose.

Beneath hopper 10 and rotatable drum 24 are a series of articles to be covered by abrasive particles emerging from the hopper. These articles are shown in the drawings as adhesive-coated discs 25 which are supported and carried forwardly in a horizontal path below hopper 10 by any suitable conveyor means, such as the disc holders 26 and L-shaped hangers 27. As indicated in Figure 2, the vertical legs of the hanger support members may be equipped with riders 28 which are moved along horizontal tracks 29 by any suitable conveyor driving means. While hanger members and disc holders are shown in the drawings, however, it will be apparent that other supporting and conveying means may be employed, depending upon the nature of the particular articles to be coated by the abrasive grains.

Between hopper l0 and the horizontal path of articles carried by hangers 27 are a pair of inclined plates 30 and 31. Each of the plates carries a support rod 32 and 33, respectiveiy, which are rotatably mounted upon a suitable frame (not shown) for pivotal adjustment of the plates along the longitudinal axes of those rods. Plate Sill is formed of a non-magnetic material such as brass or a hard plastic material. Plate 34), on the other hand, is composed of a material capable of magnetic inductance, such as soft iron. As shown in Figure l, the top edge 34- of plate fail is tapered and is positioned adjacent the curved surface of drum 2d. The tapered top edge of plate 3%) divides the stream of particles flowing through discharge opening 12 and deflected by drum 24, so that some of these particles drop along the rear surface of the plate while others are directed into the space defined by plate 3t) and the more forwardly positioned plate 31.

Below hopper ill and the conveyors 2'7 is a magnetic bed 35 composed of a set of permanent magnets aligned in parallel with the poles thereof facing in the same direction. Therefore, like poles of the magnets, such as the north poles, all face upwardly while the opposite south poles project downwardly. Magnetic lines of force emanating from this compound magnet bed orient magnetically attractable particles falling through hopper 10 and distributed by drum 24, and direct these particles upon articles carried by hanger members 27. Furthermore, the magnetic bed induces a magnetic field in the soft iron plate 30 so that this platebecomes an effective magnet itself,v and not only divides the stream of' particles flowing from hopper but also orients or preorients these particles as they drop, toward" the adhesivecoated article carried therebelow.

A conveyor belt 36 is interposed between the articles carried by hanger members. 27, and the, magnetic bed 35, and is carried by rotatable cylinders 37. The belt is preferably driven rearwardly in a directionopposite. to that of hanger support members 27 and is moved in that direction by any suitable driving means (not shown) such as anelectric motor. Belt 36 collects and carries away. abrasiveparticles which have not. settled upon discs 25, and also prevents the accumulation of such' particles upon the compound magnet bed35; As shown in Figure 2, the rotatable cylinder carrying belt 36 may be equipped with shafts 38 which are rotatably mounted upon frame members 39.

Above the most forward portion of magnet bed 35 and above articles 25 carried by horizontally movable supportmembers 27, is a pick-upbelt 40. Figure 2 shows this belt being carried by cylinders 41, 42 and 43 and having a lower portion movable in a direction transverse to the path of articles or products 25. Belt 40. passes between the articles carried by the forwardly moving support members, anda second or upper magnet bed 44 which, in cooperation with the pick-up belt, removes excess abrasive particles distributed upon the backing articles passing therebelow. Each of the magnets of bed 44 is orientediin complementary relation to the magnets of lower bed 35. That is, the magnets of both beds have their corresponding poles facingin the same general direction. While both the upper and lower magnet beds 44 and 35 are represented in the drawing as compound magnets, each composed of a plurality of parallel permanent magnets, it is to be understood that any other suitable magnetic.meanssuch as electromagnets might be used in connection with the present invention.

As abrasive-coated articles pass beneath the upper magnet bed 44, abrasive grains not adhering to the adhesive coating of those articles are attracted by the magnetic field of the upper bed and. are drawn upwardly. The lifted particles cling to that portion of the trans versely moving pick-up belt 40 which extends below magnetbed44, and are carried by the belt to atrough or chute 45. Magnet bed 44 terminates above. chute 45 so. that particles magnetically held against belt 40 are released above the chute and aredirected by that chute intoany suitable receptacle. (not shown) where they may be collectedfor. re-use in hopper 10.

While I have showneach of the magnets of lower bed 35. in verticalalignment with other magnets of the same bed, it will'be apparent that these parallel magnets might be 'angularly mounted so that the lines of force emanating therefrom are angled with respect to the discs or articles carried byhanger support members 27. If the magnets are tilted'in this manner, then the magnetically attractableabrasive particles distributed upon the backing discs 25-Will be magnetically oriented and secured thereon in corresponding angular. fashion.

The abrasive grains or granules used in connection with the present inyention may have a magnetic composition or theymay be non-magnetic particles coated with a magnetically susceptiblematerial as disclosed in my copending application, Serial No. 527,629, filed August 10, 1955. To prepare a magnetically attractable abrasive materialfrom non-magnetic grains, I first wet the surfaces of the grains with a liquid adhesive, such as urea formaldehyde or phenol formaldehyde. A powdered magnetically susceptible material such as magnetite is then dustedv upon. the. wetted surfaces. of thegrains, and

"of the backing article.

the adhesive is hardened into a solid state by heating, drying or'firing, depending upon the'particular' nature of the adhesive used. By this method, a coating of a magnetically susceptible material is applied and bound upon each of the abrasive grains or granules.

The grains are then placed in hopper 10, and shield 15 may be vertically adjusted by the rotation of nut 20 to regulate the. quantity of grains dischargedthroughopening 12 upon the rotating drum 24. The magnetically attractable grains arecarried by rotating drum 24 to the divider plate 30 Where the particles are exposed to the magnetic field induced in that soft iron plate by the lower magnet bed 35. Many of the particles discharged through opening 12 of the hopper tend to cling to-the front and back sides of the divider plate and migrate slowly toward the lower end of that plate. Deflector plate 31 acts to confine the stream of particles flowing from hopper 10, and maintains these particles within the magnetic field inducedin plate 30. Plates 30 and 31 may be pivotally adjusted to vary the intensity or concentration of the stream of particles and to control the number of particles passing on either side of the divider plate 30.

As .the magnetically responsive particles fallbetween plates 30 and 31 and drop along the sides of plate 30, they are oriented by the magnetic lines of force emanating from compound magnet bed 35 and soft iron plate 30: As shown diagrammatically in Figure 3, each of the abrasive particles is irregular in shape and is generally elongated; Therefore, when they are exposed to the magnetic lines of force, a magnetic field is induced in each of the par-' ticles. The largest end of each particle is attracted by magnet bed 35 and assumes a polarity opposite to the magnetic polarity of the top surface of bed 35. As a result, the particles are oriented so that their longitudinal axes extend in the same. direction.

Eachof the discs orarticles 25 is coated witha suitable adhesive material, such as an air-drying animal glue or a thermosetting phenolic resin. I have. foundphenol formaldehyde provides a particularly suitable adhesive coating for articles to be covered with the abrasive grains; While the glue or adhesive is still in a liquid'state, the adhesive-coated articles are carried by hanger support members 27 beneath hopper 10. The magnetically oriented grains falling between plates 30 and 31, and clinging to the. bottom edge of divider plate 30, are directed by magnet bed 35 .onto the adhesive-coated surface of'thl backing articles 25. Since they upwardly directed pointed ends of each particle have the same polarity, the particles tend to repel. each other and are, therefore, uniformly dis tributed upon the adhesive-coatedsurfac e. The spacing between each of the grains helps .to prevent clogging and contributes greatly. to the. effective. cutting operation of the abrasive article produced by the present methodand apparatus.

It isbelieved evident from the; foregoing description thatcompoundmagnet bed 35 not only-orients the abrasive particles so that. their. longitudinal axes extend'in the same direction .as themagneticlines of force emanating fromthe magnetbed, but/that the magnetic bedals'o draws each of the. particlestoward'the adhesive-coated articles 25 and firmly seatsthese particles upontheadhesive coating carried by those articles. The abrasive particles therefore arefirmly. aflixed, to the adhesivecoating despite shallows, dips or crevices upon the surface To insure proper attachment of the abrasive gnains uponthe backing articles, it-may. be desirable to employ backing articles composed of. a magnetically susceptiblematerial or which have magnetic pigments in their composition. For example, if thecloth or board material used to fashion a suitable backingarticle has a magnetically susceptible material such as magnetite or cobalt in its composition, then that. backing article will assume a. definite polarity as. it passes. over the compoundmagnet bed;35. The article i tselft would ha e duce ma e c ektw i hr d further-Raid in orienting and seating the abrasive particles upon the adhesive carried thereby. Also, the adhesive itself may contain materials having magnetic properties to further aid in directing and orienting the particles.

After the oriented particles have been distributed upon the adhesive coating of the backing articles, the adhesive is allowed to set or pass into its solid state. If the adhesive is an ordinary animal glue, then it will pass into a solid state upon drying. A thermosetting adhesive may be set by heating the adhesive to the desired temperature. Such thermosetting adhesives may be heated in ovens or by infra-red equipment as is well understood in the art.

As shown best in Figure 3, the adhesive coating 46 upon each of the backing articles 25 is preferably thick enough only to afiix one continuous layer of particles to the backing sheet. To insure a uniform single layer of particles upon the backing sheets, I have found it desirable to distribute an excess of particles upon the sheets or articles and then later remove the excess without disorienting any of the particles secured by the adhesive. This removal is accomplished by means of the upper magnet bed 44 and the pick-up belt 40. As illustrated in Figure 1, a portion of the upper bed 44 is disposed above or overlaps the lower magnet bed 35. Figure 3 diagrammatically shows a second layer of unsecured particles being lifted by the attractive forces of upper magnet bed 44, and onto the lower surface of the pick-up belt. The transversely moving pick-up belt then carries these excess particles to trough or chute 45 which extends beyond the magnetic field of compound pick-up magnet bed 44. The backing articles are therefore left with single layers of oriented abrasive particles embedded in the adhesive coating carried thereby.

While 1 have disclosed the method and apparatus of the present invention in considerable detail for purposes of illustration, it will be understood by those skilled 1n the art that many of these details may be varied considerably without departing from the spirit and scope of this invention.

I claim:

1. An apparatus for applying abrasive particles upon a backing article comprising a hopper being adapted to contain magnetically attractable abrasive particles therein and having an opening at its lower portion for the d1scharge of abrasive particles therethrough, a movable support member for supporting and carrying adhesive-covered articles in a horizontal path extending beneath the discharge opening of said hopper, driving means for horizontally moving said support member and said adhesivecovered article, a magnetizable plate between said hopper and said support member for magnetically orienting abrasive particles discharged through said opening, lower magnetic means comprising a bed of permanent magnets below said support member for magnetizing said plate and for drawing said oriented particles upon the adhesivecovered article carried by said support member, and upper magnetic means above said support member and at a spaced distance from said hopper for magnetically removing excess abrasive particles not in contact with the adhesive covering of said article.

2. An apparatus for applying abrasive grains upon a backing article comprising a hopper for containing a quantity of irregularly-shaped and generally elongated magnetically attractable abrasive grains and having a discharge opening for the discharge of said grains therefrom, a movable support member for supporting and carrying an adhesive-covered article in a horizontal path at a spaced distance beneath the discharge opening of said hopper, driving means for horizontally moving said support member and said adhesive-covered article, a magnetically inductible plate extending between said hopper and said support member for. magnetically pre-orienting abrasive grains discharged through said opening, a mag net bed below said support member comprising a plurality of upstanding permanent bar magnets having like poles thereof facing in the same direction to provide upwardly extending magnetic lines of force throughout the area of application of said grains to said adhesive-covered articles for inducing a magnetic field in said plate and for drawing the pre-oriented grains upon the article carried by said support member, whereby, as said irregularly-shaped grains pass downwardly from said hopper, said grains are gravity-oriented so that their largest ends face downwardly and are magnetically pro-oriented so that their longitudinal axes extend in the same direction.

3. In an apparatus for applying abrasive grains upon a backing article, a hopper adapted to contain a quantity of irregularly-shaped and generally elongated magnetically attractable abrasive grains and having a discharge opening for discharging said grains therefrom, a movable support member for supporting and carrying adhesivecovered articles in a horizontal path at a spaced distance beneath the discharge opening of said hopper, driving means for horizontally moving said support member and said adhesive-covered article carried thereby, a magnetically inductible plate extending between said hopper and said support member, a generally horizontal first magnet bed below said magnetically inductible plate and the horizontal path of said support member and comprising a plurality of upstanding permanent bar magnets having like poles thereof facing in the same direction for inducing a magnetic field in said plate and for drawing said magnetically attractable grains upon the adhesive-covered article carried by said support member below said plate, said first bed extending along the path of said support member and beyond the horizontal limits of the area of application of said grains upon said article, and a second horizontal magnet bed above the path of said support member for removing excess grain deposited upon said article, said second bed having a portion thereof disposed above said first bed and comprising a plurality of generally vertical permanent bar magnets having like poles thereof facing in the same direction, whereby, the generally vertical lines of force of said magnet beds maintain the grains adhering to said articles in vertical alignment as said articles pass above said :first bed and thence beneath said second bed.

4. In an apparatus for producing abrasive coated articles comprising a hopper providing a chamber adapted to contain magnetically attractable abrasive particles therein and having an opening at its lower portion for the discharge of abrasive particles therethrough, a generally horizontally movable support member for supporting and carrying adhesive-covered articles beneath the discharge opening of said hopper, driving means for moving said support member beneath said hopper, magnetic means below said hopper and said support member for magnetically directing and seating particles upon an adhesive-covered article carried by said support member, and a plate member between said hopper and said support member capable of magnetic induction to provide a magnetic field induced by said magnetic means for orienting said particles as they are discharged from said hopper.

5. The structure of claim 4 in which said magnetic means comprises at least one permanent magnet.

References Cited in the file of this patent UNITED STATES PATENTS 2,027,087 Buckner Jan. 7, 1936 2,254,531 Kirchner et al Sept. 2, 1941 2,276,328 Melton et a1 Mar. 17, 1942 2,376,342 Carlton May 22, 1945 

